1. Field of the Invention
The present invention relates to a method and apparatus for forming sheet metal and, more particularly to a method and apparatus that controls stretching of multiple gauge welded blanks during forming.
2. Description of the Related Art
Recent advancements in technology have provided blanks for stamping that are comprised of sheet metals of various gauges having different mechanical and chemical properties welded together to form a single welded blank. Conventional techniques used to weld the sheet metal components together include laser, induction, and mash welding. These welded blanks are of interest particularly to the automotive industry. Welded blanks can be formed into automotive body panels such that heavier gauge steel is positioned where strength is required, and lighter gauge steel is positioned where strength is less critical. Consequently, body panels formed from welded blanks provide weight reduction because heavier gauge material is provided only to those areas requiring additional strength. Additionally, welded blanks afford a reduction in the number of sheet metal components and welding operations required.
Conventional stamping dies, however, are generally incapable of producing satisfactory products, including automotive body panels, from welded blanks. Indeed, to produce products of satisfactory quality, it is essential to deform sheet metal blanks in a uniform manner. When conventional dies are used to form welded blanks, the lighter gauge portion of the welded blank stretches before the heavier gauge portion is subject to deformation. At a minimum, such a condition causes uneven stretch of the lighter gauge material. In the worst case, conventional dies split or wrinkle the lighter gauge material of the welded blank during forming.